Method for producing double metal cyanide (DMC) catalysts

ABSTRACT

The invention provides an improved process for the preparation of double metal cyanide (DMC) catalysts for the preparation of polyether polyols by polyaddition of alkylene oxides on to starter compounds containing active hydrogen atoms, in which aqueous solutions of a metal salt and a metal cyanide salt are first reacted in the presence of an organic complexing ligand and optionally one or more further complex-forming components to form a DMC catalyst dispersion, this dispersion is then filtered, the filter cake is subsequently washed with one or more aqueous or non-aqueous solutions of the organic complexing ligand and optionally one or more further complex-forming components by a filter cake washing and the washed filter cake is finally dried, after an optional pressing out or mechanical removal of moisture.

TECHNICAL FIELD OF THE INVENTION

The invention relates to an improved process for the preparation ofdouble metal cyanide (DMC) catalysts for the preparation of polyetherpolyols by polyaddition of alkylene oxides on to starter compoundscontaining active hydrogen atoms.

BACKGROUND OF THE INVENTION

Double metal cyanide (DMC) catalysts for the polyaddition of alkyleneoxides on to starter compounds containing active hydrogen atoms havebeen known for a long time (see, for example, U.S. Pat. No. 3,404,109,U.S. Pat. No. 3,829,505, U.S. Pat. No. 3,941,849 and U.S. Pat. No. A5,158,922). The use of these DMC catalysts for the preparation ofpolyether polyols has the effect, in particular, of a reduction in thecontent of monofunctional polyethers with terminal double bonds,so-called mono-ols, compared with the conventional preparation ofpolyether polyols by means of alkali metal catalysts, such as alkalimetal hydroxides. The polyether polyols obtained in this way can beprocessed to high-quality polyurethanes (e.g. elastomers, foams andcoatings).

DMC catalysts are usually obtained by reacting an aqueous solution of ametal salt with the aqueous solution of a metal cyanide salt in thepresence of an organic complexing ligands, e.g. an ether. In a typicalcatalyst preparation, for example, aqueous solutions of zinc chloride(in excess) and potassium hexacyanocobaltate are mixed anddimethoxyethane (glyme) is than added to the dispersion formed. Afterfiltration and washing of the catalyst with aqueous glyme solution, anactive catalyst of the general formula

Zn₃[Co(CN)₆]₂.x ZnCl₂.y H₂O.z glyme

is obtained (see e.g. EP-A 700 949).

According to the prior art, DMC catalysts are prepared e.g. by mixingaqueous solutions of a metal salt (preferably of a zinc salt, such ase.g. zinc chloride) and a metal cyanide salt (e.g. potassiumhexacyanocobaltate) in the presence of an organic complexing ligand(preferably tert-butanol) and optionally further ligands in a stirredtank to form a dispersion. The catalyst is isolated from the dispersionby known techniques, preferably by centrifugation or filtration. Toachieve a sufficiently high catalyst activity it is necessarysubsequently to wash the catalyst with an aqueous ligand solution.Water-soluble by-products, such as e.g. potassium chloride, which canreduce the activity of the catalyst, are removed from the catalyst bythis washing step. According to the prior art this washing step iscarried out by redispersing the catalyst in an aqueous ligand solution,e.g. in a stirred tank, with subsequent renewed isolation of the solidby e.g. centrifugation or filtration. To obtain highly active DMCcatalysts it is in general necessary to wash the catalyst at least oncemore, non-aqueous ligand solutions preferably being used for the furtherwashing operations. According to the prior art the further washing stepsare also carried out by redispersing with subsequent isolation of thecatalyst. Finally, the DMC catalyst must be dried. This form of catalystpreparation is exceptionally time-consuming and cost-intensive. Processtimes of more than 100 hours are required for preparation of DMCcatalysts on a commercial scale (see e.g. U.S. Pat. No. 5,900,384).Because of the high catalyst costs, the profitability of theDMC-catalysed process of polyether polyol preparation is thereforeconsiderably impaired.

SUMMARY OF THE INVENTION

It has now been found that highly active DMC catalysts can be obtainedby a considerably simplified process in which aqueous solutions of ametal salt and a metal cyanide salt are first reacted in the presence ofan organic complexing ligand a) and optionally one or more furthercomplex-forming components b) to form a DMC catalyst dispersion, thisdispersion is then filtered, the filter cake is subsequently washed by afilter cake washing and the washed filter cake is finally dried, afteroptional pressing out or mechanical removal of moisture.

This improved process for the preparation of catalysts avoids theseveral re-dispersions of the catalyst, with subsequent isolation,required according to the prior art to date for the preparation ofhighly active DMC catalysts and therefore leads to a considerableshortening of the process times for preparation of DMC catalysts. DMCcatalysts which are prepared by the new, improved process have acomparable activity to DMC catalysts which are prepared in asignificantly more expensive manner according to the prior art to date.

DESCRIPTION OF THE INVENTION

The present invention therefore provides an improved process for thepreparation of double metal cyanide (DMC) catalysts, in which aqueoussolutions of a metal salt and a metal cyanide salt are first reacted inthe presence of an organic complexing ligand a) and optionally one ormore further complex-forming components b) to form a DMC catalystdispersion, this dispersion is then filtered, the filter cake issubsequently washed with one or more aqueous or non-aqueous solutions ofthe organic complexing ligand a) and optionally one or more furthercomplex-forming components b) by a filter cake washing and the washedfilter cake is finally dried, after an optional pressing out ormechanical removal of moisture.

The double metal cyanide compounds contained in the DMC catalysts whichare suitable for the process according to the invention are the reactionproducts of water-soluble metal salts and water-soluble metal cyanidesalts.

Water-soluble metal salts which are suitable for the preparation of thedouble metal cyanide compounds preferably have the general formula (I)

M(X)_(n)  (I),

wherein M is chosen from the metals Zn(II), Fc(II), Ni(II), Mn(II),Co(II), Sn(II), Pb(II), Fe(III), Mo(IV), Mo(VI), Al(III), V(V), V(IV),Sr(II), W(IV), W(VI), Cu(II) and Cr(III). Zn(II), Fe(II), Co(II) andNi(II) are particularly preferred. The X are identical or different,preferably identical anions, preferably chosen from the group consistingof halides, hydroxides, sulfates, carbonates, cyanates, thiocyanates,isocyanates, isothiocyanates, carboxylates, oxalates or nitrates. Thevalue for n is 1, 2 or 3.

Examples of suitable water-soluble metals salts are zinc chloride, zincbromide, zinc acetate, zinc acetylacetonate, zinc benzoate, zincnitrate, iron(II) sulfate, iron(II) bromide, iron(II) chloride,cobalt(II) chloride, cobalt(II) thiocyanate, nickel(II) chloride andnickel(II) nitrate. Mixtures of different water-soluble metal salts canalso be employed.

Water-soluble metal cyanide salts which are suitable for the preparationof the double metal cyanide compounds preferably have the generalformula (II):

(Y)_(a)M′(CN)_(b)(A)_(c)  (II),

wherein M′ is chosen from the metals Fe(II), Fe(III), Co(II), Co(III),Cr(II), Cr(III), Mn(II), Mn(III), Ir(III), Ni(II), Rh(III), Ru(II),V(IV) and V(V). M′ is particularly preferably chosen from the metalsCo(II), Co(III), Fe(II), Fe(III), Cr(III), Ir(III) and Ni(II). Thewater-soluble metal cyanide salt can comprise one or more of thesemetals. The Y are identical or different, preferably identical alkalimetal cations or alkaline earth metal cations. The A are identical ordifferent, preferably identical anions chosen from the group consistingof halides, hydroxides, sulfates, carbonates, cyanates, thiocyanates,isocyanates, isothiocyanates, carboxylates, oxalates or nitrates. Botha, and b and c are integers, the values for a, b and c being chosen suchthat electroneutrality of the metal cyanide salt exists; a is preferably1, 2, 3 or 4; b is preferably 4, 5 or 6; c preferably has the value 0.Examples of suitable water-soluble metal cyanide salts are potassiumhexacyanocobaltate(III), potassium hexacyanoferrate(II), potassiumhexacyanoferrate(III), calcium hexacyanocobaltate(III) and lithiumhexacyanocobaltate(III).

Preferred double metal cyanide compounds contained in the DMC catalystsare compounds of the general formula (III)

M_(x)[M′_(x′)(CN)_(y)]_(z)  (III),

wherein M is as defined in formula (I) and M′ is as defined in formula(II), and x, x′, y and z are integers and are chosen such thatelectroneutrality of the double metal cyanide compound exists.Preferably, x=3, x′=1, y=6 and z=2, M=Zn(II), Fe(II), Co(II) or Ni(II)and M′=Co(III), Fe(III), Cr(III) or Ir(III).

Examples of suitable double metal cyanide compounds are zinchexacyanocobaltate(III), zinc hexacyanoiridate(III), zinchexacyanoferrate(III) and cobalt(II) hexacyanocobaltate(III). Furtherexamples of suitable double metal cyanide compounds are to be found e.g.in U.S. Pat. No. 5,158,922. Zinc hexacyanocobaltate(II) is particularlypreferably used.

Organic complexing ligands a) which can be employed in the processaccording to the invention are water-soluble organic compounds withheteroatoms, such as oxygen, nitrogen, phosphorus or sulfur, which canform complexes with the double metal cyanide compound. Suitable organiccomplexing ligands are e.g. alcohols, aldehydes, ketones, ethers,esters, amides, ureas, nitriles, sulfides and mixtures thereof.Preferred organic complexing ligands are water-soluble aliphaticalcohols, such as ethanol, isopropanol, n-butanol, iso-butanol,sec-butanol and tert-butanol. tert-Butanol is particularly preferred.

The organic complexing ligand a) is added either during the preparationof the catalyst or directly after formation of the dispersion of thedouble metal cyanide compound. The organic complexing ligand a) isusually employed in excess.

DMC catalysts which are preferred for the process according to theinvention are those which, in addition to the organic complexing ligandsa) mentioned above, also comprise one or more further organiccomplex-forming components b). This component b) can be chosen from thesame classes of compounds as complexing ligand a). Component b) ispreferably a polyether, polyester, polycarbonate, glycidyl ether,glycoside, carboxylic acid ester of polyhydric alcohols, polyalkyleneglycol sorbitan ester, a bile acid or salt, ester or amide thereof, acyclodextrin, organic phosphate, phosphite, phosphonate, phosphonite,phosphinate or phosphinite, an ionic surface- or interface-activecompound or an α,β-unsaturated carboxylic acid ester. DMC catalysts withsuch ligand combinations are described e.g. in EP-A 700 949, EP-A 761708, WO 97/40086, WO 98/08073, WO 98/16310, WO 99/01203, WO 99/19062, WO99/19063 or German Patent Application 19905611.0.

The DMC catalysts which are suitable for the process according to theinvention can optionally also comprise water and/or one or morewater-soluble metal salts of the formula (I) from the preparation of thedouble metal cyanide compound.

The DMC catalysts according to the invention are conventionally preparedin aqueous solution by reaction of metal salts, in particular of theformula (I), with metal cyanide salts, in particular of the formula(II), organic complexing ligands a) and optionally one or more furthercomplex-forming components b).

The aqueous solutions of the metal salt (e.g. zinc chloride, employed instoichiometric excess (at least 50 mol %, based on the metal cyanidesalt)) and of the metal cyanide salt (e.g. potassium hexacyanocobaltate)are preferably first reacted here in the presence of the organiccomplexing ligand a) (e.g. tert-butanol), a dispersion forming.

The organic complexing ligand a) can be present here in the aqueoussolution of the metal salt and/or other metal cyanide salt, or it isadded directly to the dispersion obtained after precipitation of thedouble metal cyanide compound.

Preferably, the dispersion formed is then also treated with one or morefurther complex-forming components b). The further complex-formingcomponent b) is preferably employed here in a mixture with water andorganic complexing ligand a).

The DMC catalyst dispersion can be prepared e.g. in a stirred tank,optionally by the process variant described in U.S. Pat. No. 5,891,818,in which some of the catalyst dispersion prepared in stirred reactor iscirculated and sprayed into the reactor headspace and the circulatingstream here is passed though a “high shear in-line mixer”.

However, the DMC catalyst dispersion is preferably prepared using amixing nozzle (e.g. a smooth jet nozzle, Levos nozzle, Bosch nozzle andthe like), particularly preferably a jet disperser, such as is describedin German Patent Application 199 58 355.2.

In a smooth jet nozzle a first educt stream is first accelerated in anozzle and atomized at a high flow rate into a slowly flowing secondeduct stream. Mixing of the two educt streams then takes place via theturbulent disintegration of the resulting jet into eddies of differentsize (eddy cascade). Compared with the stirred tank, concentrationdifferences can be broken down significantly faster in this manner,since significantly higher and more homogeneous output densities can beachieved.

However, a jet disperser should preferably be employed for the processaccording to the invention. The jet disperser can be constructed suchthat two nozzles are arranged in series. A first educt stream is firstaccelerated to high degree in the first nozzle due to the narrowing incross-section. The accelerated jet sucks up the second component herebecause of the high flow rate. The resulting jet is than passed from themixing chamber through further nozzles arranged perpendicular to thedirection of the first educt stream. The distance between the nozzleswill preferably be chosen such that because of the short residence time,only seed formation but not crystal growth takes place in the mixingchamber. The rate of seed formation of the solid is thus decisive forthe optimum design of the jet disperser. A residence time of 0.0001 s to0.15 s, preferably 0.001 s to 0.1 s is favourably established. Thecrystal growth takes place only in the outflow. The diameter of thefurther nozzles should preferably be chosen such that furtheracceleration of the partly mixed educt streams takes place there.Because of the shear forces which additionally occur in the furthernozzles as a result, the state of homogeneous mixing is achieved by afaster eddy disintegration in a shorter time compared with a smooth jetnozzle. As a result, even in precipitation reactions with a very highrate of seed formation is possible to achieve the state of ideal mixingof the educts, so that it is possible to establish definedstoichiometric compositions during the precipitation reaction. Nozzlediameters of 5,000 μm to 50 μm, preferably 2,000 μm to 200 μm haveproved favourable at pressure losses in the nozzle of 0.1 bar to 1,000bar or output densities in the range from 1*10⁷ W/m³ to 1*10¹³ W/m³.

n nozzles (where n=1-5) can be arranged in succession, depending on thedesired particle size, so that a multi-stage jet disperser is obtained.The additional advantage of further dispersers is that particles whichhave already formed can be comminuted mechanically by the high shearforces in the nozzles. It is possible in this manner to prepareparticles with diameters of 20 μm to 0.1 μm. Instead of having severalnozzles arranged in series, however, the comminution can also beachieved by circulating the dispersion.

Other mixing organs for the preparation of dispersions, such as aredescribed in EP-A 101 007, WO 95/30476 or German Patent Application 19928 123.8, or combinations of these mixing organs can also be employed.

Heating of the dispersion may occur due to the energy dissipation in thenozzles and the crystallization enthalpy. Since the temperature can havea considerable influence on the crystal formation process, a heatexchanger can be installed downstream of the mixing organ for anisothermal process procedure.

Problem-free scale-up is possible, for example, by the use of arelatively large number of bores, arrangement of several mixing organsin parallel or enlargement of the free nozzle area. However, the latteris not achieved by increasing the nozzle diameter, since the possibilityof emergence of a core stream exists in this manner, the result of whichis a deterioration in the mixing result. Slits with an appropriate areaare therefore preferably to be employed in the case of nozzles withlarge free nozzle areas.

The DMC catalyst dispersion formed is then separated off by filtration.Many filter devices suitable for mechanically separating off liquids canin principle be employed for this. Suitable filter devices aredescribed, for example, in “Ullmann's Encyclopaedia of IndustrialChemistry”, vol. B 2, chapters 9 and 10, VCH, Weinheim, 1998 and H.Gasper, D. Oechsle, E. Pongratz (ed.): “Handbuch der industriellenFest/Flüssig-Filtration [Handbook of Industrial Solid/LiquidFiltration”, Wiley-VCH Verlag GmbH, Weinheim, 2000.

The pressure gradient needed for the filtration can be applied here bygravity, by centrifugal force (e.g. filter centrifuges), preferably by agas pressure difference (e.g. vacuum filter or pressure filter) or byliquid pressure (e.g. filter presses, drum or disc filters and possiblytransverse flow filtration modules). The subsequent filter cake washingcan be carried out by mashing or, preferably, by a flow-through washing.In this case the washing liquid flows through the cake and the liquidpreviously contained in the cake is displaced, diffusion effects alsobecoming effective here. The removal of moisture from the washed cakecan be effected by a gas pressure difference, centrifugal force ormechanical pressing, or preferably by a combination of a moistureremoval by a gas pressure difference with subsequent mechanical pressingout. The pressure for the mechanical pressing out can be applied hereeither mechanically or by membranes.

Both discontinuously and continuously operated filter devices can beemployed for separating off the catalysts. Examples of discontinuouslyoperating filter devices are trailing blade and turned-down filtercentrifuges, membrane, chamber, frame or tubular filter presses,pressure filter machines, autopress devices, disc pressure, multipletube and plate filters and vacuum and pressure suction filters. Examplesof continuously operating filter devices are screen conveyor presses,pressure and vacuum drum filters, pressure and vacuum disc filters,conveyor belt filters and transverse flow filters.

Vacuum or pressure filters or suction filters are particularly suitablefor filtration of the DMC catalyst dispersion on a laboratory scale, andpressure suction filters, filter presses and pressure filter machinesare particularly suitable on a technical and industrial scale.

Membrane filter presses have proved to be particularly suitable on apilot plant and technical scale. With the aid of a suitable filtercloth, preferably a membrane cloth, these allow filtration of the DMCcatalyst dispersion on the basis of a liquid pressure gradient applied.The subsequent filter cake washing preferably takes place as aflow-through washing in the filter press, in order thus to simplify andtherefore accelerate the preparation process. The preferred ratio ofwash liquid to filter cake volume lies in the amounts which effectcomplete exchange of the amount of liquid present in the original filtercake. The mechanical removal of moisture from the filter cake whichfollows washing of the filter cake and is preferably to be carried outbefore the drying can preferably be effected in the filter press,preferably by mechanical pressing out by a pressure applied to themembranes. The mechanical removal of moisture preferably leads to assubstantial as possible a removal of the wash liquid from the filtercake.

The filtration is in general carried out at temperatures of 10 to 80° C.The pressure differences applied can be 0.001 bar to 200 bar, preferably0.1 bar to 100 bar, particularly preferably 0.1 bar to 25 bar, thepressure difference applied depending on the device employed.

After the filtration the moist filter cake (residual moisture in general30-95 wt. %) is washed, optionally after prior pressing out ormechanical removal of moisture, by suitable devices. This washing ispreferably carried out on the filter device with one or more aqueous ornon-aqueous solutions of the organic complexing ligand a) and optionallyone or more further complex-forming components b) by a flow-throughwashing, in which the filter cake is not dispersed in the liquid and thewashing effect takes place by the solutions flowing through the filtercake and optionally overlapping diffusion effects.

The moist filter cake is preferably first washed with an aqueoussolution of the organic complexing ligand a) (e.g. tert-butanol).Water-soluble by-products, such as e.g. potassium chloride, can beremoved from the catalyst in this manner. The amount of organiccomplexing ligand a) in the aqueous washing solution is preferably 40 to80 wt. %, based on the total solution. It is furthermore preferable toadd to the aqueous washing solution some further complex-formingcomponent b), preferably 0.5 to 5 wt. %, based on the total solution.

After this first washing step, further washing steps with aqueous ornon-aqueous solutions of the organic complexing ligand a) and optionallyone or more further complex-forming components b) can follow, theselikewise being carried out according to the invention as a filter cakewashing. The activity of the catalyst can be increased further by thismeans. However, it has been found that a single washing of the filtercake with an aqueous solution of the organic complexing ligand a) andoptionally one or more further complex-forming components b) by a filtercake washing is often already sufficient to obtain DMC catalysts with anexceptionally high activity.

A significant reduction in the total amount of washing solution to beemployed is often possible in the process according to the invention,compared with the processes of the prior art, so that the processaccording to the invention also leads to a reduction in the materialcosts of preparation of DMC catalysts.

The amount of washing liquid employed, based on the filter cake volume,is in general 0.5/l to 1,000/l, preferably 1/l to 500/l (in each casebased on the volume), particularly preferably precisely the amount ofwashing liquid necessary for as complete as possible a replacement ofthe liquid originally present in the filter cake. The filter cakewashing is in general carried out at temperatures of 10 to 80° C.,preferably 15 to 60° C.

The filter cake washing is carried out under pressures of 0.001 bar to200 bar, preferably 0.1 bar to 100 bar, particularly preferably 0.1 barto 25 bar.

The washing times are some minutes to several hours.

It has proved advantageous to press out the washed filter cake, afterthe filter cake washing, under pressures of 0.5 to 200 bar, preferablyunder pressures which are as high as possible. This can be carried oute.g. directly after the filter cake washing, in a filter press or bymeans of other suitable pressing devices which allow application of amechanical pressure, so that the liquid present in the filter cake canescape through a membrane or a suitable filter cloth.

The DMC catalyst is then dried at temperatures of about 20 to 120° C.under pressures of about 0.1 mbar to normal pressure (1,013 mbar).Contact dryers and convection dryers and also spray dryers are suitablefor this. Drying can optionally also be carried out directly in thedevices for mechanically separating off liquid if these are suitable forthis (e.g. suction dryer, centrifuge dryer and “hot filter press”).

The present invention also provides the use of the DMC catalystsprepared by the process according to the invention in a process for thepreparation of polyether polyols by polyaddition of alkylene oxides onto starter compounds containing active hydrogen atoms.

A significant shortening of the process times of the preparation of DMCcatalysts compared with the prior art is possible by this improvedpreparation process for DMC catalysts. Since DMC catalysts which areprepared by the new, improved process have a comparable activity in thepreparation of polyether polyols to that of DMC catalysts which areprepared in a considerably more expensive manner by the prior art todate, this leads to a considerably increased profitability of theDMC-catalysed process for the preparation of polyether polyols.

Because of their exceptionally high activity, the DMC catalysts preparedby the process according to the invention can often be employed in verylow concentrations (25 ppm and less, based on the amount of polyetherpolyol to be prepared). If the polyether polyols prepared in thepresence of the DMC catalysts prepared by the process according to theinvention are used for the preparation of polyurethanes, removal of thecatalyst from the polyether polyol can be omitted without the productqualities of the polyurethane obtained being adversely influenced.

EXAMPLES

Preparation of the Catalyst

Example 1 Comparison Example: Catalyst A

(Preparation of the Catalyst with a Single Washing of the Filter Cake byRedispersing with Subsequent Filtration)

A solution of 81.25 g zinc chloride in 810 g distilled water iscirculated at 45° C. in a loop reactor which comprises a jet disperser(1 bore of diameter 0.7 mm). A solution of 26 g potassiumhexacyanocobaltate in 200 g distilled water is metered into this. Thepressure loss in the jet disperser here is 2.5 bar. Directly after theprecipitation a mixture of 325 g tert-butanol and 325 g distilled wateris metered in and the dispersion is circulated for 80 min at 45° C.under a pressure loss in the jet disperser of 2.5 bar. A mixture of 6.5g cholic acid sodium salt, 6.5 g tert-butanol and 650 g distilled wateris then metered in and the dispersion is subsequently circulated for 20min under a pressure loss in the jet disperser of 2.5 bar. The solid isisolated by filtration over a vacuum suction filter. The moist filtercake is then washed with a mixture of 13 g cholic acid sodium salt, 455g tert-butanol and 195 g distilled water by circulation in the loopreactor for 20 min at 45° C. under a pressure loss in the jet disperserof 2.5 bar. The solid is filtered again over a vacuum suction filter andthe moist filter cake is then dried at 100° C. for 5 h under a highvacuum.

Example 2 Comparison Example: Catalyst B

(Preparation of the Catalyst with Washing of the Filter Cake Twice byRedispersing with Subsequent Filtration)

A solution of 81.25 g zinc chloride in 810 g distilled water iscirculated at 45° C. in a loop reactor which comprises a jet disperser(1 bore of diameter 0.7 mm). A solution of 26 g potassiumhexacyanocobaltate in 200 g distilled water is metered into this. Thepressure loss in the jet disperser here is 2.5 bar. Directly after theprecipitation a mixture of 325 g tert-butanol and 325 g distilled wateris metered in and the dispersion is circulated for 80 min at 45° C.under a pressure loss in the jet disperser of 2.5 bar. A mixture of 6.5g cholic acid sodium salt, 6.5 g tert-butanol and 650 g distilled wateris then metered in and the dispersion is subsequently circulated for 20min under a pressure loss in the jet disperser of 2.5 bar. The solid isisolated by filtration over a vacuum suction filter. The moist filtercake is then washed with a mixture of 13 g cholic acid sodium salt, 455g tert-butanol and 195 g distilled water by circulation in the loopreactor for 20 min at 45° C. under a pressure loss in the jet disperserof 2.5 bar. The solid is filtered again over a vacuum suction filter andthe moist filter cake is finally washed once again with a mixture of 4.8g cholic acid sodium salt, 650 g tert-butanol and 65 g distilled waterby circulating in the loop reactor for 20 min at 45° C. under a pressureloss in the jet disperser of 2.5 bar. After renewed filtration over avacuum suction filter, the washed, moist filter cake is dried at 100° C.for 5 h under a high vacuum.

Example 3 Catalyst C

(Preparation of the Catalyst with a Single Filter Cake Washing)

A solution of 81.25 g zinc chloride in 810 g distilled water iscirculated at 45° C. in a loop reactor which comprises a jet disperser(1 bore of diameter 0.7 mm). A solution of 26 g potassiumhexacyanocobaltate in 200 g distilled water is metered into this. Thepressure loss in the jet disperser here is 2.5 bar. Directly after theprecipitation a mixture of 325 g tert-butanol and 325 g distilled wateris metered in and the dispersion is circulated for 80 min at 45° C.under a pressure loss in the jet disperser of 2.5 bar. A mixture of 6.5g cholic acid sodium salt, 6.5 g tert-butanol and 650 g distilled wateris then metered in and the dispersion is subsequently circulated for 20min under a pressure loss in the jet disperser of 2.5 bar. 350 g of thisdispersion are filtered in a pressure suction filter under an increasedpressure of 2.0 bar. The moist filter cake in the pressure suctionfilter is then washed under an increased pressure of 3.0 bar with amixture of 2 g cholic acid sodium salt, 70 g tert-butanol and 30 gdistilled water by a filter cake washing. The washed, moist filter cakeis dried at 100° C. for 5 h under a high vacuum.

Example 4 Comparison Example: Catalyst D

(Preparation of the Catalyst with Washing of the Filter Cake Twice byRedispersing with Subsequent Filtration)

A solution of 1.625 kg zinc chloride in 16.2 kg distilled water iscirculated at 35° C. in a loop reactor which comprises a jet disperser(110 bores of diameter 0.7 mm). A solution of 0.52 kg potassiumhexacyanocobaltate in 4.0 kg distilled water is metered into this. Thepressure loss in the jet disperser here is 1.2 bar. Directly after theprecipitation a mixture of 6.5 kg tert-butanol and 6.5 kg distilledwater is metered in and the dispersion is circulated for 20 min at 35°C. under a pressure loss in the jet disperser of 1.2 bar. A mixture of0.13 kg cholic acid sodium salt, 0.13 kg tert-butanol and 13.0 kgdistilled water is then metered in and the dispersion is subsequentlycirculated for 10 min under a pressure loss in the jet disperser of 0.1bar. The solid is filtered in a membrane filter press under an increasedpressure of 2.0 bar and pressed out under 4.0 bar. The moist,pressed-out filter cake is then washed with a mixture of 0.26 kg cholicacid sodium salt, 9.1 kg tert-butanol and 3.9 kg distilled water bycirculating in the loop reactor for 20 min at 35° C. under a pressureloss in the jet disperser of 1.8 bar. The solid is filtered again in amembrane filter press under an increased pressure of 2.0 bar and pressedout under 4.0 bar, and the moist, pressed-out filter cake is finallywashed once again with a mixture of 0.096 kg cholic acid sodium salt, 13kg tert-butanol and 1.3 kg distilled water by circulating in the loopreactor for 20 min at 35° C. under a pressure loss in the jet disperserof 1.8 bar. After renewed filtration in a membrane filter press under2.0 bar and pressing out of the filter cake under 4.0 bar, the moist,pressed-out filter cake is dried at 100° C. for 5 h under a high vacuum.

Example 5 Catalyst E

(Preparation of the Catalyst with a Single Filter Cake Washing)

A solution of 1.625 kg zinc chloride in 16.2 kg distilled water iscirculated at 35° C. in a loop reactor which comprises a jet disperser(110 bores of diameter 0.7 mm). A solution of 0.52 kg potassiumhexacyanocobaltate in 4.0 kg distilled water is metered into this. Thepressure loss in the jet disperser here is 1.2 bar. Directly after theprecipitation a mixture of 6.5 kg tert-butanol and 6.5 kg distilledwater is metered in and the dispersion is circulated for 20 min at 35°C. under a pressure loss in the jet disperser of 1.2 bar. A mixture of0.13 kg cholic acid sodium salt, 0.13 kg tert-butanol and 13.0 kgdistilled water is then metered in and the dispersion is subsequentlycirculated for 10 min under a pressure loss in the jet disperser of 0.1bar. The solid is filtered in a membrane filter press under an increasedpressure of 2.0 bar. The moist filter cake in the membrane filter pressis then washed under an increased pressure of 2.5 bar with a mixture of0.22 kg cholic acid sodium salt, 8.0 kg tert-butanol and 3.4 kgdistilled water by a filter cake washing and the washed filter cake isthen pressed out under an increased pressure of 5.0 bar. The moist,pressed-out filter cake is dried at 100° C. for 5 h under a high vacuum.

Preparation of Polyether Polyols

General Procedure

50 g polypropylene glycol starter (molecular weight=1,000 g/mol) and 5mg catalyst (25 ppm, based on the amount of polyether polyol to beprepared) are initially introduced into a 500 ml pressure reactor underan inert gas (argon) and are heated up to 105° C., while stirring. 10 gpropylene oxide are then metered in all at once. Further propylene oxideis only metered in again when an accelerated drop in pressure in thereactor is observed. This accelerated drop in pressure indicates thatthe catalyst is activated. The remaining propylene oxide (140 g) is thenmetered in continuously under a constant overall pressure of 2.5 bar.When metering of the propylene oxide is complete and after anafter-reaction time of 2 hours at 105° C., volatile contents aredistilled off at 90° C. (1 mbar) and the mixture is then cooled to roomtemperature.

The resulting polyether polyols are characterized by determination ofthe OH numbers, the double bond contents and the viscosities.

The course of the reaction was monitored with the aid of time/conversioncurves (propylene oxide consumption [g] v. reaction time [min]). Theinduction time was determined from the point of intersection of thetangent at the steepest point of the time/conversion curve with theextended base line of the curve. The propoxylation times, which aredecisive for the catalyst activity, correspond to the period of timebetween activation of the catalyst (end of the induction period) and theend of metering of the propylene oxide.

Example 6 Comparison: Preparation of Polyether Polyol with Catalyst A(25 ppm)

Propoxylation time: 31 min Polyether polyol: OH number (mg KOH/g): 28.7Double bond content (mmol/kg): 6 Viscosity 25° C. (mPas): 882

Example 7 Comparison: Preparation of Polyether Polyol with Catalyst B(25 ppm)

Propoxylation time: 20 min Polyether polyol: OH number (mg KOH/g): 28.9Double bond content (mmol/kg): 5 Viscosity 25° C. (mPas): 893

Example 8 Preparation of Polyether Polyol with Catalyst C (25 ppm)

Propoxylation time: 19 min Polyether polyol: OH number (mg KOH/g): 29.3Double bond content (mmol/kg): 5 Viscosity 25° C. (mPas): 887

Example 9 Comparison: Preparation of Polyether Polyol with Catalyst D(25 ppm)

Propoxylation time: 19 min Polyether polyol: OH number (mg KOH/g): 29.2Double bond content (mmol/kg): 6 Viscosity 25° C. (mPas): 832

Example 10 Preparation of Polyether Polyol with Catalyst E (25 ppm)

Propoxylation time: 20 min Polyether polyol: OH number (mg KOH/g): 28.9Double bond content (mmol/kg): 6 Viscosity 25° C. (mPas): 869

What is claimed is:
 1. A process for preparing a double-metal cyanidecatalyst comprising: 1) combining a) at least one aqueous solution of atleast one metal salt; with b) at least one aqueous solution of at leastone metal cyanide salt; in the presence of c) tert-butanol and cholicacid sodium salt, in a manner such that a double-metal cyanide catalystdispersion is formed; 2) filtering the double-metal cyanide catalystdispersion in a manner such that a filter cake is obtained; 3) washingthe filter cake at least once with at least one organic complexingligand by a filter-cake washing; 4) mechanically removing moisture inthe washed filter cake; and 5) drying the filter cake.
 2. A process forpreparing a double-metal cyanide catalyst comprising: 1) combining a) atleast one aqueous solution of at least one metal salt; with b) at leastone aqueous solution of at least one metal cyanide salt; in the presenceof c) at least one organic complexing ligand; in a manner such that adouble-metal cyanide catalyst dispersion is formed; 2) filtering thedouble-metal cyanide catalyst dispersion in a manner such that a filtercake is obtained; 3) washing the filter cake at least once with aqueoussolutions of tert-butanol and cholic acid sodium salt by a filter-cakewashing; 4) mechanically removing moisture in the washed filter cake;and 5) drying the filter cake.
 3. A process for preparing a double-metalcyanide catalyst comprising: 1) combining a) at least one aqueoussolution of at least one metal salt: with b) at least one aqueoussolution of at least one metal cyanide salt; in the presence of c) atleast one organic complexing ligand; in a manner such that adouble-metal cyanide catalyst dispersion is formed; 2) filtering thedouble-metal cyanide catalyst dispersion in a manner such that a filtercake is obtained; 3) washing the filter cake at least once withnon-aqueous solutions of tert-butanol and cholic acid sodium salt by afilter-cake washing; 4) mechanically removing moisture in the washedfilter cake; and 5) drying the filter cake.
 4. The process of claim 1 inwhich the metal salt is zinc chloride.
 5. The process of claim 1 inwhich the metal cyanide salt is potassium hexacyanocobaltate.
 6. Theprocess of claim 1 in which steps 2 and 3 are conducted in a filterpress.
 7. The process of claim 1 in which steps 2, 3 and 4 are conductedin a filter press.
 8. The process of claim 1 in which the combination iscarried out with a mixing nozzle.
 9. The process of claim 8 in which themixing nozzle is a jet disperser.
 10. The process of claim 2 in whichthe metal salt is zinc chloride.
 11. The process of claim 2 in which themetal cyanide salt is potassium hexacyanocobaltate.
 12. The process ofclaim 2 in which steps 2 and 3 see conducted in a filter press.
 13. Theprocess of claim 2 in which steps 2, 3 and 4 are conducted in a filterpress.
 14. The process of claim 2 in which the combination is carriedout with a mixing nozzle.
 15. The process of claim 14 in which themixing nozzle is a jet disperser.
 16. The process of claim 3 in whichthe metal salt is zinc chloride.
 17. The process of claim 3 in which themetal cyanide salt is potassium hexacyanocobaltate.
 18. The process ofclaim 3 in which steps 2 and 3 are conducted in a filter press.
 19. Theprocess of claim 3 in which steps 2, 3 and 4 are conducted in a filterpress.
 20. The process of claim 3 in which the combination is carriedout with a mixing nozzle.
 21. The process of claim 20 in which themixing nozzle is a jet disperser.